Just in time for Halloween: An article from NATIONAL GEOGRAPHIC about parasites in the animal kingdom that "zombify" their hosts:Mindsuckers
For example: The jewel wasp's sting turns a cockroach into a "zombie" that the wasp can lead into a burrow by its antenna. The roach passively allows the wasp to lay an egg on its underside and stays motionless while the larva hatches and digs into its abdomen. Another kind of wasp inserts its egg into the abdomen of a ladybug, which goes about its normal behavior while being gradually eaten from inside by the wasp larva. When the larva crawls out of the ladybug and spins a cocoon, the insect remains "enthralled." Immobilized by the alien chemicals in its brain, it stands guard over the cocoon. When the adult wasp emerges and flies away, the ladybug dies. Gypsy moth caterpillars sometimes get infected by a microbe called a baculovirus. When it comes time for the virus to leave its host, it changes the behavior of the caterpillar, causing the insect to climb to the tops of leaves. Then the virus dissolves the caterpillar into "goo," which drops onto leaves below where the next generation of immature moths will ingest it. Killifish infected by certain flatworms tend to gravitate to the surface of the water, thus exposing them to getting eaten by birds, the next stage in the flatworm's life cycle. The single-celled parasite Toxoplasma, to complete its life cycle by moving from rats to cats, causes infected rats to lose their fear of feline odor and even become attracted to the smell of cat urine.
Although the hosts do behave in a zombie-like manner, because they haven't actually died they seem more like possessed creatures than undead (with the possible exception of the unfortunate ladybug, which continues a gruesome pseudo-life with its guts being devoured). While the hosts may be compared to zombies in their mindless behavior, the parasites remind me of many fictional vampires with their mind-altering abilities. I'm gratified to learn that there could be an authentic biological basis for my premise that my own vampires secrete chemicals in their saliva to have soothing, euphoric, and addictive effects on victims.
Creatures like the ones described in the article irresistibly bring to mind Octavia Butler's classic story "Bloodchild." Human colonists on an alien planet have agreed to a symbiotic partnership with the sapient inhabitants, who seem to resemble giant centipedes. Almost all female (they're apparently suffering a shortage of males), they need human hosts (mainly male) to incubate their eggs, which are laid inside the man's body. Normally, the mother removes her offspring when they hatch before they can hurt or kill the host. But sometimes she doesn't get there in time . . . . These aliens' stingers inject a chemical that eases pain and induces a calm, pleasant emotional state. The female alien in the story acts as a patron to a human family, of whom she seems genuinely fond.
Many fictional vampires enter symbiotic relationships with human blood donors, especially in romances. But would a human community plausibly become desperate enough to make a bargain like the one in "Bloodchild"? Possibly, if the alternative is certain death for all of them.
Margaret L. CarterCarter's Crypt